Although the first useful lasers were developed in the 1960s, recent advances in laser and fiber optic delivery systems have greatly enhanced the use of this technology in the field of medicine. Today there are numerous types of laser systems designed for operation in a wide range of applications primarily related to surgical procedures.
A common type of laser known as a CO2 laser delivers radiation with a wavelength of 10.64 microns. However, in order to focus or channel the radiation produced by a CO2 laser it is necessary to configure sets of mirrors in certain ways. These systems are typically large and expensive. With the advent of the YAG type laser, it became possible to generate and focus the 1.064 micron wavelength laser radiation through a silica core optical fiber. Thus, fiber optic surgical tools have become standard in certain procedures and the range of their utility is still being explored and discovered.
Laser scalpels are used in different ways, including incision, necrosis or killing of live tissue, removal of tissue or structure, and cauterization of tissue. During incision and removal of tissue, a beam of laser radiation causes an instantaneous vaporization of the water molecules in the tissue contacted by the beam. The tissue seems to disappear with a puff of steam, leaving behind a very small amount of charred tissue. This process is called ablation, or more specifically photoablation, a term which refers to the removal of live, diseased or dead tissue by vaporization. Incision is accomplished using a very narrow beam directed to a small point drawn across the tissue being incised. A very focused beam would provide the greatest amount of control during either operation.
Cauterization and necrosis of living tissue is accomplished or coagulation, more specifically, by photocoagulation of contacted or penetrated tissue. In this modality, the laser beam causes the proteins in the contacted tissue to heat up rapidly and thermally denature. This essentially kills and seals living tissue and blood vessels. The process has been likened to frying an egg. In practice, during an incision procedure cauterization of the incised tissue is likely to occur simultaneously. Thus, laser surgery is often characterized by a lack of bleeding during the operation.
The process which occurs during an operation depends upon the technique and the type of radiation being used. Typically, although light at 10.64 is strongly absorbed by the H2O molecule resulting in efficient incision or ablation of tissue, a surgeon may be able to defocus the light beam and decrease the intensity of the radiation, with a resulting effect of cauterization. Similarly, a YAG type laser can be used to cauterize. Since light at 1.064 microns is not strongly absorbed by water molecules the radiant energy scatters and overall surface coagulation would occur. However, a fiber optic delivery system is capable of creating a very small focal point with a very narrow beam, and therefore, incision or ablation is also possible.
In the prior art there are described devices which generate a dual wavelength beam of radiation and are thereby capable of both cutting and cauterizing. There also exist inventions which deliver energy at much shorter wavelengths, such as 250-350 nm. At these wavelengths proteins, as opposed to water molecules, absorb the radiation. These systems, however, are less suitable for general types of surgical operations since they are more complicated to operate. Use of such systems has not become standard in most medical facilities and their cost is generally too high to justify their purchase for occasional use in fairly specialized procedures.
The construction of optical fibers used in surgical procedures is fairly simple. A plastic or silicone cladding is often used to protect the quartz fiber which itself transmits the laser radiation. Transmission of the radiant beam is possible since the beam is constrained to the core of the fiber. Very few photons escape the fiber. The technology related to the use of silica fibers in medical lasers is well known, e.g. B. P. McCann, Photonics Spectra, May 1990, pp 127-136. Differences between these types of optical fibers and those used in telecommunications and data transmission are important. Several design factors must be considered such as sterilizability, quartz core integrity and purity, power capacity and index of refraction of materials of construction.
Generally, 20 to 100 watts of energy are used to perform soft tissue surgery. A scalpel used externally might be operated in a much different manner than a scalpel used in internal surgery. An angle firing apparatus is very important when a cystoscope or other type of endoscope is used. The scalpels used with most types of endoscopes are very small. Additionally, often laser surgery is performed with irrigation by a cooling gas or liquid to cool the scalpel firing tip as well as to prevent the tissue from overheating. Internal surgery techniques generally use liquids, such as a saline solution. Additionally, liquids are more practical since containment of gases poses certain restrictions tool design. Therefore, often a cystoscope will have multiple channels or will be large enough to accommodate a viewing port or camera, a scalpel, an irrigation supply and vacuum channel to remove the coolant.
Delivery of high power radiation can have a very damaging effect on the scalpel itself. One of the problems with existing designs is that the tip which directs the laser beam at a right angle becomes overheated. This is caused by an absorption of power (heat) at the reflecting surface. Overheating of the firing tip can be caused by fouling of the firing tip itself, an accumulation of incompletely burned tissue which rapidly heats up and can trigger a process known as thermal runaway. As heat rapidly builds up the firing tip melts or crumbles away. Often, angle firing surgical scalpels will need to be replaced partway through the surgical operation due to this problem.
Thermal runaway can be avoided by providing a transparent, hard tip, such as sapphire or quartz. An alternative is to provide a highly reflective surface in the scalpel tip for directing the beam. One material capable of being polished to a very high reflectance is gold. Other materials could be used. If more of the incident radiation is reflected less will be absorbed and the temperature at the surface will not rise too high, especially using today's advanced lasers with pulsed energy, high-peak pulsing and temperature detecting fiber tip protection systems. Additionally, encasing the firing tip in some more durable material, such as stainless steel, would help preserve firing tip integrity. In the prior art, the reflective surface is part of the firing tip and is therefore difficult, if not impossible, to polish.
Another solution to the problem of thermal instability is to provide at least one vent or hole in the firing tip of the scalpel. As the reflected beam is directed to the side, steam is generated by the cooling irrigation fluid in a direction normal to the reflected surface (the hot surface). Providing convection cooling vents on the side opposite the opening for the reflected beam will draw the cooling solution into the firing tip of the scalpel and increase heat dissipation from the firing tip. In operation the cooling fluid would have the effect of cooling both the firing tip and the tissue directly in beam contact.
A scalpel which could be adjusted to provide the precise amount of cooling ability would be very useful. For example, if during a single operation, the surgeon first wished to coagulate a large amount of tissue, an instrument which delivered lower power radiation for relatively long periods of time would need to be well irrigated to prevent overheating from extended use. Thus large cooling vents could be necessary in the firing tip of such a scalpel. Then, to vaporize the tissue the surgeon could increase the power output of the scalpel and vaporize the coagulated tissue in short duration, high powered operation. Unless the flowrate of cooling water could be reduced, the vaporization step would be impossible. As described above, the two different processes of coagulating and ablation require different surgical operating parameters.
Another problem associated with current laser scalpels is that they are often clumsy to use and difficult to manipulate precisely. One problem is that the quartz fiber is so thin it is difficult to grasp effectively, especially if it is used in conjunction with a cystoscope or some type of endoscope where the firing end cannot be controlled directly by the surgeon. Also, as the scalpel is rotated and manipulated by the surgeon, the fiber becomes twisted under a certain amount of angular torque. It would be desirable to provide a scalpel which would be easily controlled, perhaps through the use of some external control means.
Many surgical operations are standard and the procedures followed are routine and well known in the field. For example, in prostate surgery to reduce an enlargened prostate, a typical surgical procedure using a laser scalpel would be to fire energy at four specific anatomic zones causing ablation in very precisely delimited areas in the prostate gland itself. Since the four points procedure is common it would be desirable to provide the surgeon with a scalpel which would select consecutively the exact points of laser beam contact, making the operation safer and less prone to surgeon error.
The following describes the method for performing a prostatectomy, the removal of tissue from an enlarged prostate gland. Using a laser scalpel, the tissue to be removed is coagulated to kill the tissue. This results in an immediate swelling of the surrounding tissue. Therefore, a catheter is allowed to remain in place for several days following the operation to allow for drainage of urine. Once the swelling subsides, the catheter is removed and over a period of several weeks the dead tissue sloughs off naturally. It would be desirable to provide a scalpel which would allow the surgeon to remove the swollen, coagulated tissue by vaporization during the same operation to avoid the need for a catheter completely. As discussed above, radiation at 1.064 microns is not readily absorbed by water molecules. It appears that the high-peak power output laser is capable of generating higher temperatures useful for vaporization at the surface.
It would be desirable to have an angle firing scalpel which would not overheat and lose integrity and efficiency. It would also be desirable to have an angle firing scalpel which could both cut tissue and perform the cauterization process, either simultaneously or by the surgeon's control. Such a scalpel should be appropriately sized to be convenient to use. It is believed that the present invention meets these needs.